Regulated progression through the cell division cycle is important to maintain the stability of the genome and to prevent uncontrolled cell division. The steps of the cell cycle are ordered by an underlying transcriptional program, which coordinates the expression of genes with the times in the cycle when their functions are needed. This tightly regulated pattern of gene expression is disrupted in nearly all cancer cells, underscoring its importance. High-throughput genomic approaches have identified TF networks that control cell cycle- regulated gene expression in diverse eukaryotes, the best understood being the yeast Saccharomyces cerevisiae. The prevailing model suggests that key TFs at each stage of the cell cycle activate expression of downstream TFs to drive the cell cycle forward. However, this model does not accurately predict many of the downstream effects that are observed when individual TFs are inactivated or deleted. A greater understanding of the coordination between TF proteins in the network is needed to fully understand this fundamental mechanism of cell-cycle control. Here we will address this outstanding issue by characterizing the response of each cell cycle TF (and their downstream effectors) to defined environmental or genetic perturbations. In the first aim, we will elucidate the dynamics of changes in the expression, regulation, and activity of each TF in the network in response to environmental conditions that we have found alter TF phosphorylation by cyclin- dependent kinase (Cdk1). In the second aim, we will dissect the mechanisms underlying how multisite phosphorylation of each TF in the network impacts their functions. In addition, we will use systematic, saturating mutagenesis in combination with bulk competition assays to elucidate how phosphorylation of multiple residues within an unstructured region of a model TF is read out into a change in TF function. By examining multiple regulatory parameters of this TF network in detail, our work will lead to an integrated, mechanistic view of this network, and have a significant impact on our understanding of cell-cycle control.